A review of the dynamics and control of ammonia emissions in cropping systems

Ammonia volatilization after nitrogen fertilization represents a major pathway of reactive nitrogen loss in cropping systems, reducing nitrogen use efficiency and contributing to environmental impacts. This review analyses fertilizer-based strategies to mitigate these losses from a mechanistic perspective, focusing on the processes governing ammonia formation and emission under field conditions. Approaches such as urease inhibition, pH regulation, ammonium retention, and controlled-release formulations are examined in relation to their effects on hydrolysis, chemical equilibria, and mass transfer. Evidence from field studies and meta-analyses shows strong variability in mitigation performance across soils, climates, and management practices, indicating a high dependence on local conditions. The analysis also identifies trade-offs between nitrogen loss pathways, where reductions in ammonia emissions may influence nitrous oxide emissions or nitrate leaching. A process-based framework is proposed to guide the selection of mitigation strategies according to dominant loss mechanisms, supporting more efficient and context-specific nitrogen management in cropping systems.